In vivo synthesis of cellulose by Acetobacter xylinum was monitored by darkfield light microscopy. Cellulose is synthesized in the form of a ribbon projecting from the pole of the bacterial rod. The Cellulose biosynthesis by Acetobacter xylinum has been widely investigated (1)(2)(3)(4)(5)(6). It is generally believed that the synthesis of microfibrils occurs by an extracellular process involving the sequential addition of glucose residues to the growing tips at a distance from the cell (5-7). The biochemical reactions of cellulose synthesis have been extensively documented, the intermediate products being hexose phosphates (8), sugar nucleotides (9), and perhaps glycolipids (6). However, recent findings from kinetic data (1) and biochemical incorporation studies using defined cell wall extracts (2-4) indicate a closer relationship than previously expected between the bacterial envelope and the cellulose polymer.The purpose of this investigation is to clarify and lay groundwork on the cytology of cellulose formation in Acetobacter xylinum. In order to achieve this, we have carefully observed the dynamics of the in vWo process, using darkfield and Nomarski interference microscopy. We (Fig. 1)
ZHANG, M. I. N., and WILLISON, J. H. M. 1987. An improved conductivity method for the measurement of frost hardiness.Can. J. Bot. 65: 710-715. A suspension culture of Bromus inermis Leyss was grown under a variety of conditions to provide a range of frost hardiness. The growth conditions involved both low-temperature treatment and the addition of abscisic acid to the culture medium. Frost hardiness (LT,,, i.e., subzero temperature causing 50% mortality) was estimated by both fluorescein diacetate vital staining and by a conventional method involving estimation of ion leakage from frost-damaged cells by measurement of the conductivity of a bathing solution. It was found that the latter method always underestimated the frost hardiness by comparison with the former. Evidence that the vital staining estimates were reliable is presented. A subsequent time-course study of ion leakage from frost-stressed cultures showed that leakage increased with time of immersion in deionized water, and that the extent of the difference was dependent upon the growth conditions and the minimum temperature experienced. Analysis of the experimental data showed that this ion leakage differential can be used to estimate LT,, reliably by comparison with the vital staining estimates, and it is proposed that the protocol might be useful as an improved standard method in testing the frost hardiness of plant tissues. The physiological basis for this test is discussed. ZHANG, M. I. N., et WILLISON, J. H. M. 1987. An improved conductivity method for the measurement of frost hardiness.Can. J. Bot. 65 : 710-715. Une suspension de cellules de Bromus inermis Leyss a Ct C cultivCe sous diverses conditions d'endurcissement au gel. Les conditions de croissance comportaient un traitement 2 basse tempCrature et l'addition d'acide abscisique au milieu de culture. La rksistance au gel (TL,,, i.e., la temperature sous zCro causant 50% de mortalit&) fut CvaluCe par deux mCthodes differentes : la coloration vitale avec le diacCtate de fluorescCine et la conductivitC Clectrique de la solution, mesurant la sortie des ions des cellules, suite aux dommages causCs par le gel. L'on trouvC que cette demibre mCthode, comparativement B la premzre, sousestimait l'endurcissement au gel. Une preuve de la fiabilitC de la coloration vitale est prCsentCe. Une Ctude subsCquente des temps de sortie des ions, chez les cellules ayant subi le gel, a montrC que la perte d'ions augmentait avec le temps d'immersion dans l'eau dCsionisCe, et que l'importance de la diffkrence dCpendait des conditions de croissance et de la tempkrature minimale subie. L'analyse des risultats a rev616 que cette difference de sortie d'ions peut Ctre utiliske de faqon fiable pour la TL,, en comparaison avec les valeurs estimCes de la coloration vitale. L'on propose que le protocole pourrait Ctre utile en tant que mCthode uniformisCe et amCliorCe dans les essais d'endurcissement au gel des tissus vCgCtaux. La base physiologique de la mCthode est discutCe.
. 1992. F,lectrical impedance analysis in plant tissues: The effect of freeze-thaw injury on the electrical properties of potato tuber and carrot root tissue.Can. J. Plant Sci.72: [545][546][547][548][549][550][551][552][553]. Electrical impedances in the range 100 Hz to 800 KHz were measured in potato tubers and carrot root cortex both before and after freeze-thaw cycles. These impedance data were analyzed using equivalent circuit modelling based on complex nonlinear least squares (CNLS) (Zhang and Willison l99la). After freezing to and thawing from -3, -6, -9 and -12oC, carrot root tissues were best characterized by a double shell model composed of extracellular resistance, cytoplasmic resistance, plasma membrance capacitance, vacuole interior resistance, and tonoplast capacitance. Although freeze-thaw cycles to -3 or -6'C did not kill the carrot tissues, extracellul,ar resistance and vacuole interior resistance were halved relative to control tissues, and cytoplasmic resistance decreased to a third ofthe control value. Plasma membrane capacitance and tonoplast capacitance were not affected by the -3 and -6"C noninjurious stresses. After carrot root or potato tuber tissues had been killed by freezing (-3'C for potato tuber and -18'C for carrot), the tissues were best represented by a single-shell model composed of extravesicular resistance, intravesicular resistance, and vesicle membrane. Compared with unfrozen controls, freeze-killed potato tubers were characterized by a 30-fold decrease in extracellular resistance, a7-fold decrease in intracellular resistance, and a l0-fold decrease in plasma membrane capacitance. Freeze-killed carrot roots were characterized by a 30-fold decrease in extracellular resistance, 3-fold decrease in intracellular resistance, and 3.5-fold decrease in plasma membrane capacitance. These results are compatible with massive rupturing of protoplasts during lethal freeze-thaw injury. (CNLS). Aprds des gels de -3, -6, -9 et -12'C,les tissus d6gel6s de carotte pouvaient se caract6riser par un moddle ir deux enveloppes compos6 de r6sistance extracellulaire, r6sistance cytoplasmique, capacitance de la membrane plasmatique, r6sistance intra-vacuolaire et capacitance des tonoplastes.Bien que des gels de -3 ou de -6'C n'aient pas tu6 les tissus, la r6sistance extracellulaire et la r6sistance intra-vacuolaire 6taient r6duites de moiti6 par rapport 2r celles des tissus t6moins et Ia r6sistance cytoplasmique 6tait r6duite des deux tiers. La capacitance de la membrane plasmatique et celle des tonoplastes n'dtaient pas affect6es par ces stress non destructeurs. Aprbs gel destructeur (-3"C pour la pomme de terre et -l8'C pour la carotte), les tissus pouvaient s'adapter )r un moddle ir enveloppe simple com-
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